Thin film metal alloy magnetic recording disks typically comprise a substrate, such as an aluminum-magnesium (AlMg) alloy with a nickel-phosphorous (NiP) surface coating, a cobalt-based alloy sputter deposited as the magnetic layer on the substrate, and a protective overcoat, such as a sputter-deposited amorphous carbon film, formed on the magnetic layer. Such disks may also include a sputter-deposited underlayer, such as a layer of chromium (Cr), chromium-vanadium (CrV) or tungsten (W), between the substrate and the magnetic layer, and a sputter-deposited adhesion layer, such as a Cr, W or titanium (Ti) layer, between the magnetic layer and the protective overcoat. A general description of the structure of such thin film disks is given in U.S. Pat. Nos. 4,610,911 to Opfer et al., and 4,552,820 to Lin et al.
One of the problems with such disks is the suitability of the protective overcoat to provide corrosion resistance for the underlying magnetic layer and resistance to wear caused by contact of the disk by the air-bearing slider which carries the magnetic recording head. Protective overcoats of amorphous carbon formed by the sputtering of a graphite target in the presence of pure argon (Ar), such as described in U.S. Pat. No. 4,503,125 to Nelson et al., have not been proven to provide the magnetic layer with satisfactory corrosion resistance.
Amorphous hydrogenated carbon films formed by chemical vapor deposition (CVD) plasma decomposition of hydrocarbon gases or reactive sputtering of a graphite target in an atmosphere of argon and hydrocarbon gases have been suggested as suitable for use as thin film disk protective overcoats. Japanese Kokai No. 60-155668 describes a protective overcoat formed by sputtering carbon in an atmosphere of various hydrocarbon gases, and Japanese Kokai No. 60-157725 describes a protective overcoat formed by sputtering a carbon target in the presence of various hydrocarbon gases or a mixture of such hydrocarbon gases with Ar, helium (He) or hyrogen (H.sub.2).